DAS systems serve to distribute radio signals in buildings or in other contiguous areas, such as a university campus or company campus, shopping centers, pedestrian zones, stadiums, hospitals, etc. In DAS systems an identical radio signal is radiated in different locations. A distinction is made in the industry between so-called passive and active DAS systems. In a passive DAS system, the RF signal from a base station is supplied to the antennas via coaxial connections and via splitters and tappers. Active DAS system have an active distribution of the signals over large distances, e.g. via coaxial cables, subsequent to which the signals are then distributed by a further coaxial installation to various passive or active antennas.
A conventional passive DAS system for transceiving radio signals from a mobile communication provider is represented on the left side of FIG. 1. The left side of FIG. 1 shows a first base station 60-1 connected to a plurality of antenna elements 50-1 via a distribution system or distributor network 40-1. The antenna elements 50-1 are connected to the distributor network 40-1 via a splitter or tapper 42-1. The radio signals from the base station 60-1 are forwarded and transmitted via the distributor network 40-1 to the antenna elements 50-1 via the splitters/tappers 42-1.
In order to take into account current broad-band requirements, LTE works for example with several parallel input and output signals. This technology is referred to as MIMO (multiple input multiple output). In order to implement a MIMO system, it is required in a conventional installation to provide further, parallel distributor paths and distributor connections and to install an additional antenna infrastructure, as shown on the right-hand side of FIG. 1.
The right-hand side of FIG. 1 shows a second base station 60-2 for the LTE signals, which is likewise connected to several second antenna elements 50-2 via a second distributor network 40-2. The second radio signals are forwarded from the second base station 60-2 via the second distributor network 40-2 and the splitters/tappers 42-2 to the second antenna elements 50-2 and transmitted. The effort to install this additional antenna infrastructure is substantial, since the second distributor network 40-2 must be laid for example across fire-protection sections and through ceilings and walls. The second radio signals cannot be transmitted via the existing first distributor network 40-1, since the second radio signal are either two radio signals working in the same frequency range or the first distributor network 40-1 is not configured for the frequency range of the second radio signals.
In the discussion above, FIG. 1 also shows a further known embodiment with a MIMO architecture. For the sake of simplicity, for the representation of the MIMO architecture a third base station 60-3 has been added (shown as dashed lines). Typically, the two MIMO channels are implemented within the base station 60-3 and connected to the two distributor networks 40-1 and 40-2. In the MIMO architecture the first base station 60-1 and the second base station 60-2 are not present. This MIMO architecture also requires the second distributor network 40-2 with the disadvantages described above.
An international patent application No. WO 2011/086921 (Panasonic Corporation) is known in the art, which discloses a so-called relay device for forwarding radio signals via a distributor network. The distributor network in this international application comprises a converter that converts all incoming radio signals from one frequency to a different frequency, so that the radio signals can be transmitted via the distributor network, and a second converter that converts the transmitted signals back to the original frequency.